Every day on TV, radio, newspapers and magazines, we come across situations that involve calculating percentages. Interest rates on vehicle financing, installment purchases, discounts on cash purchases, income of savings, high of the dollar, are some examples of where we observe the use of the calculation of the percentage of a number. In every financial transaction we can notice the presence of a percentage, increasing or decreasing the value of something. But what is a percentage?
Percentage is a part of a whole of one hundred parts, that is, a fraction whose denominator is 100. Note the examples that follow.
Example 1. Out of a group of 100 kids, 75 of them like soccer. The fraction that represents the number of boys in this group who enjoy soccer is: 75/100
As this fraction represents a part of the total of 100 boys, it represents a percentage of this group. Every fraction with denominator 100 can be written as a percentage. Watch:
So, we can say that 75% of these kids like football.
Example 2
Thus, we can say that:
46% of children born in Brazil are female.
As stated, any and all fractions with a denominator of 100 can be written as a percentage. This feature makes it easy to calculate the percentage of a number. See the next example.
Example 3. In an ice cream parlor, 30% of the 250 ice creams sold per day are strawberry flavored. How many strawberry ice cream are sold per day in this ice cream parlor?
Solution: The problem states that 30% of 250 ice creams are strawberry. So we must know how much is 30% of 250 to answer the problem.
In mathematics, the word “of” represents the multiplication operation. So, we can rewrite the statement as follows:
30% of 250 = 30% x 250
We saw in the previous examples that:
So we can improve the statement writing once again:
Soon, the ice cream shop sells 75 strawberry ice creams a day.
We saw that percentage is a different way of writing a fraction whose denominator is 100. As every fraction can be written in the form of a decimal number, the percentage can also be written. Let's see how this happens.
Writing the percentage in decimal form can make calculations easier in solving some problems. Watch:
Example 4. Pedro saved 12% of his salary in savings. Knowing that Pedro's salary is R$1500.00, how much did he invest in savings?
Solution: According to the problem, Pedro saved 12% of 1500 in savings. Thus, we will have:
12% of 1500 = 12% × 1500
But,
The calculation is as follows:
12% × 1500 = 0,12 × 1500 = 180
Therefore, Pedro saved 180 reais in savings.
Example 5. How much is 23% of 500?
Solution: We know that:
23% = 0,23
Thus, we will have:
23% of 500 = 0.23 × 500 = 115
By Marcelo Rigonatto
Mathematical
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